The present invention relates to a method and device for controlling printed valuable or security items, in particular banknotes.
For example, the invention may be used for controlling postage stamps, treasury bonds, postal orders, identity papers, passports, and any item, in general, printed using methods in which the various printing steps cannot be performed in line with one another, and the printing quality of which is to be controlled. In the following description, reference is made purely by way of example to banknotes.
As is known, banknotes are produced from special sheets (typically comprising watermarks and/or metal bands) large enough to accommodate several finished banknotes, and,which are subjected to various printing steps, using different printing methods, to obtain the various graphic and alphanumeric characters.
More specifically, printing may comprise some or all of the following steps:
a) Offset printing. This is performed out of line with the edge of the sheet, which therefore cannot be used as a reference by which to determine the coordinates of the offset-printed details. Offset printing is normally performed on both sides of the sheet.
b) Copperplate printing. This is performed at high pressure, may be displaced with respect to the offset printing, and slightly deforms the paper, thus possibly resulting in inclination of the copperplate with respect to the offset printing. Copperplate printing may only be performed on the front or both sides (front-back) of the banknote, and may comprise several steps, each of which may be horizontally/vertically misaligned or inclined with respect to the others and with respect to the offset printing.
c) Silk-screen printing. Like copperplate printing, this may be displaced or inclined with respect to the offset printing.
Following the above printing steps, the printed sheet is quality controlled, and only the passed banknotes are printed with serial numbers. Finally, the sheet is cut to separate the banknotes, but cutting is not performed in line with any of the printed details.
Quality control is currently performed manually to ensure the various printed details conform closely enough with an ideal value, and that there are no errors in colouring (too much ink or none at all), no smudges, etc.
At present, there is no way of automatically controlling the print quality of banknotes, in that, to take into account the numerous variables involved, the deviation thresholds used to compare the banknote with a specimen image would have to be so high that even banknotes with serious errors in colouring would be passed.
Automatic control systems do exist for validating, discriminating between, or determining the deterioration of banknotes already in circulation, but which provide for examining only a very small portion of the note (typically a narrow horizontal intermediate strip through significant parts of the overall design). The information supplied by such systems is therefore insufficient for quality control purposes, in which case the inking defects and smudges for detection are normally localized.
It is an object of the present invention to provide a control method and device enabling reliable, automatic control.
According to the present invention, there is provided a method of controlling valuable or security items, in particular banknotes, characterized by comprising the steps of:
a) acquiring a controlled-item image;
b) acquiring a predetermined characteristic of said controlled-item image;
c) acquiring a specimen-item image having said predetermined characteristic; and
d) comparing said controlled-item image with said specimen-item image.
According to the present invention, there is also provided a device for controlling banknotes, characterized by comprising first acquisition means for acquiring a controlled-item image; second acquisition means for acquiring a predetermined characteristic of said controlled-item image; third acquisition means for acquiring a specimen-item image having said predetermined characteristic; and comparing means for comparing said controlled-item image with said specimen-item image.